Mild eruptive activity continued in April; stronger at the beginning and end of the month, less vigorous 4-20 April. Southern Crater sub-continuously emitted small to moderate amounts of pale gray (and occasionally brown) ash and vapor. Several emissions of blue vapor occurred. Crater glow and weak incandescent lava ejections were occasionally seen during more active periods. Roaring, rumbling, and loud booming were heard. Pale grey, rather than the usual white, emissions occurred from Main Crater, indicating ash entrainment and a possibly significant change in activity. Seismicity showed no trends during the month. Daily totals of volcanic earthquakes were steady at ~1,500, and event amplitudes were about the same as in March. Tilt measurements suggested that slight radial inflation (<1 µrad) may have occurred in April.

Geological Summary. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical basaltic-andesitic stratovolcano to its lower flanks. These valleys channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most observed eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Information Contacts: C. McKee and P. Lowenstein, RVO.